Presentation on theme: "ECOSYSTEM JELLO… Kerim Aydin Bob Francis Pat Livingston."— Presentation transcript:
ECOSYSTEM JELLO… Kerim Aydin Bob Francis Pat Livingston
Ecosystem properties “Stability” Many Many terms –Resilience –Resistance Food web structure? –Diversity –High biomass or other adaptations in susceptible groups MEASURE VARIANCE
Need to understand control TOP DOWN? BOTTOM UP? MIDDLE OUT? –Which (if any) is dominant in marine systems?? –Explanations may be easy to find and hard to confirm!
“Kitchellization” The process of losing beer money by making poor guesses about ecosystem responses Phytoplankton Zooplankton Forage Fish Large Fish Marine MammalsSharks ???
“Revenge??” Phytoplankton Zooplankton Forage Fish Large Fish Marine MammalsSharks
Top-down-bottom-up-ENSO- PDO-fishing? Figure the Frequency!!!
Where can you go from a marine food web? Food Webs Process models Investigate specific environmental linkages Address species concerns (endangered spp.) Multi-species harvest models Predict returns from harvest strategies Biomass dynamics models Measure broad ecosystem properties Assess risks of regime shifts Determine the need for mechanisms
Why use the most general models? Regimes Happen! There needs to be a way to abstract ecosystems, and look for risks. This is one example of using “whole ecosystem properties” to examine this risk. Biomass dynamics models Measure broad ecosystem properties Assess risks of regime shifts Determine the need for mechanisms
Food web forcing? Phytoplankton Zooplankton Forage Fish Large Fish Marine MammalsSharks ????
This experiment Start with two “Actual” Food Webs The East. Bering Sea Shelf system with pollock as the dominant fished species The East. Tropical Pacific Tuna are dominant fished species Both have shown interannual variation in primary production which may be linked to climate signals. The East. Bering Sea Shelf system with pollock as the dominant fished species The East. Tropical Pacific Tuna are dominant fished species Both have shown interannual variation in primary production which may be linked to climate signals.
Need rules for species interactions One possibility of many: –P/B then B of predator respond to increases of prey biomass –“overly stable” - only looking for chances of regimes –Ratio-dependent predator/prey model with satiation (ECOSIM based) –Mimics surplus production (Pella-Tomlinson) model when predator, prey fixed. –Next step is to add better age-structure (single biggest weakness of the model). ????
Dynamics of overlap B i - V ij V ij BjBj v ij V ij v ij (B i -V ij ) a ij V ij B j dV ij /dt = v ij (B i -V ij ) - v ij V ij - a ij V ij B j Assume fast equilibrium for Vij V B-V “It’s cold down there!”
The appearance of Density Dependence dV ij /dt = v ij (B i -V ij ) - v ij V ij - a ij V ij B j = 0 V ij = v ij B i /(2* v ij + a ij B j ) C ij (B i,B j ) = a ij v ij B i B j (2* v ij + a ij B j ) Predator Biomass C ij (or M instant ) Prey biomass C ij /B j
P/B vs. Trophic Level - EBS (note missing microzooplankton) B vs. Trophic Level? No firm relationship…
One theoretical explanation... Simply hitting the resonant frequencies of each model component? –Useful for model (and real life) analysis of important terms. –“Real life” P/B values may imply natural resonant frequencies.
Small observations Missing seasonal/micronekton Frequencies, P/B are the same unit (1/time) Trophic Level less of a fit
Fish must follow history or be history If P/B of a species is in the range that it is “excited” by the balance of top-down/bottom up, does it need extra biomass to be stable (“avoid” regimes)? We don’t know the frequency of primary production variation in many systems. Need to look at more ecosystems
What responds to each frequency range? Forage fish, micronekton response peaks near ENSO-scale forcing. –This doesn’t mean that they vary on an ENSO scale, but that they are most susceptible to crashes when the bottom-up forcing is at that scale.
What responds to each frequency range? Forage fish, micronekton response peaks near ENSO-scale forcing. Larger commercial fish response peaks at “regime” (10-50 year) forcing.
So what about fishing? General principle of surplus production As B goes down, P/B goes up, due to: more food per fish smaller, faster growing fish P P B B P/B
Are our fish becoming anchovies? Beyond “multispecies MSY”, have we changed the natural time scale of animals (P/B, replacement, generation time) without changing the natural time scale (frequency) of input variation?
Shift happens (with a little help from…) Fishing may push a species in or out of the high CV range. –Will regime changes occur MORE or LESS frequently with fishing? –It can occur in both directions: the fin whale control? –What is the range of fishing change compared to natural variability in P/B?
Preliminary until... More ecosystems and parameters Devil in the details Model type, (L.V., ECOSIM, Spatial, parameters) Fishing changes (historical) Still, true for “reasonable” forms Middle-out Forcing
CONCLUSIONS The frequency of primary production variation may be strongly connected to P/B. The frequency associated with regime shifts (10-50 year period) is the frequency at which most currently fished species show the strongest response. Fishing may push P/B into or out of the range of greatest variation, depending on the frequency of natural forcing in the ecosystem.
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